1. Field of the Invention
The present invention relates to the field of production of wafers and the field of display technology, and more particularly, to a thin-film transistor (TFT) and a method for forming for the TFT.
2. Description of the Prior Art
With rapid development of technology, the monitor display technology applying to cellphones, flat panels, or computers improves and updates constantly. The flat panel display (FPD) technology representing liquid crystal displays (LCD) has developed and improved rapidly with the outbreak of the technology and the demand of the market since 1990s. Especially, thin film transistor liquid crystal displays (TFT-LCD) become the mainstream products in the FPD market because of the advantages of good performance, suitable for mass production, good automation, low raw costs, etc.
The TFT-LCD is one type of active array LCD. Each of the liquid crystal pixels on the monitor of this type is driven by the TFT arranged behind the pixels. The TFT influences response and color of the displays greatly. The TFT is an important component in such a type of displays.
The TFT, short for thin film transistor, comprises a TFT-etched back channel and a TFT-protected back channel. The TFT-etched back channel comprises a substrate, a gate, a gate insulating layer, a semiconductor layer, and a source/drain layer arranged the semiconductor layer and the gate insulating layer (a drain and a source) arranged from bottom and top. The source/drain layer is formed at the position corresponding to the semiconductor layer after the source/drain layer is deposited on the gate insulating layer and the semiconductor layer through wet-etching. The semiconductor layer is easily destroyed since strong acid and mixtures are used in the process of wet-etching.
As for the TFT components, the semiconductor layer is mostly fabricated from a-IGZO thin films. A-IGZO thin films have advantages of high carrier mobility, high stability, and good homogeneity and have a good prospect in application widely. However, it is reported that agents like water, oxygen, and light easily affects the TFT when contacting the a-IGZO thin films. That's why more and more technicians use the TFT-protected back channel and arrange a protection layer on the semiconductor layer. The main difference between the TFT-protected back channel and the TFT-etched back channel is that an etching block layer is arranged on the semiconductor layer. The etching block layer is used for protecting the semiconductor layer from being destroyed in the process of etching. But, it is necessary to add a process of fabricating the etching block layer, which affects production efficiency. Moreover, the performance of the semiconductor layer is easily affected because of the process of depositing the etching block layer on the semiconductor layer. Also, the size of the TFT expands while the designing space reduces because of the addition of the etching block layer.
A variety of TFTs are developed in the conventional technology. However, in order to improve the performance of the TFT, prolong the lifespan of the TFT, expand the designing space of the TFT array, and improve the method for forming for the TFT, it is necessary to propose a new TFT for resolving the problems occurring in the conventional technology and propose a method for forming for the new TFT.